1. Field of the Invention
The present invention relates to a wax for thermal ink transfer, and an ink composition comprising such a wax and a coloring matter.
2. Description of the Prior Art
In recent years, there have been remarkable developments in thermal ink transfer type printers or facsimiles by virtue of their merits such as simplicity in handling and low costs. In such printers or facsimiles, it is common to employ a thermal ink transfer type recording medium in the form of a ribbon or sheet, which comprises a substrate and a thermal transfer ink coated thereon and composed essentially of a wax and a coloring agent.
The thermal ink transfer type recording medium is so designed that when pressed with a heating element such as a thermal head, the thermal transfer ink layer is melted and transferred in the pattern of a heat-pressed image onto a paper sheet to form a record. Thus, the properties of the thermal transfer ink, particularly the properties of the wax as an essential component of the ink, affect the performance of the recording system to a large extent.
As such a wax, there have been used natural waxes such as carnauba wax, montan wax, Japan wax, beeswax, ceresin wax and spermaceti, and synthetic waxes such as petroleum wax, low molecular weight polyethylene and oxidized wax.
However, in the conventional thermal transfer inks using these waxes, the dispersibility of the pigment was inadequate. Further, they had drawbacks such that the heat of fusion was as high as at least about 40 cal/g, and the thermal shrinkage was relatively great, whereby the printed images tended to be unclear, and the printing speed was slow because a substantial energy was required for the melting of the ink layer.
The present inventors have conducted extensive research with an aim to develop a wax suitable for thermal ink transfer, and have finally accomplished the present invention.